1. Field of the Invention
The present invention relates to a load sensor, a method of detecting a load and a pedestrian protection system of a vehicle that employs a load sensor and a method of detecting a load.
2. Description of the Related Art
A pedestrian protection system for a vehicle usually includes an optical fiber sensor and an object examining ECU (electronic control unit). The optical fiber sensor includes an LED (light emitting diode), a photo diode and an optical fiber. The optical fiber is disposed at a front bumper of a vehicle to conduct the light of the LED to the photo diode.
If the front bumper hits an object, the optical fiber is crushed. Consequently, the rate of the light conduction loss in the optical fiber drawn from the LED to the photo diode changes, and the output current of the photo diode changes. The output current is converted into a voltage signal, which is converted into digital data. The digital data are inputted into the object examining ECU, which examines if the hit object is a pedestrian or not. If it is a pedestrian, the object examining ECU operates a pedestrian protection system, such as a pedestrian protecting airbag system.
However, the rate of the light conduction loss of the optical fiber is not proportional to the magnitude of the load that crushes the optical fiber. In other words, the magnitude of the load is not a linear function of the rate of the light conduction loss. Accordingly, it is difficult to detect an accurate magnitude of load or to discriminate a pedestrian from others with a single amplifier that has only one gain for voltage signals inputted thereto.
U.S. Pat. No. 6,739,177B2 discloses a gas sensor in which an arrangement for accurately amplifying non-linear voltage using a map. However, it is necessary to have extra means and software for map matching, which raises the cost of the load sensor.